Dacheng Tao Xuelong Li Xindong Wu Stephen J. Maybank Geometric Mean for Subspace Selection. 260-274 2009 31 IEEE Trans. Pattern Anal. Mach. Intell. 2 http://dx.doi.org/10.1109/TPAMI.2008.70 db/journals/pami/pami31.html#TaoLWM09